1. Field of the Invention
This invention relates to the field of the bending of pipe and in particular to the support of the inner wall of the pipe during bending to aid and maintain a smooth interior surface of the pipe at the bending section.
2. Background Art
When laying pipe, it is nearly always required to bend the pipe so as to change its direction. It is a common practice to support the inner wall of the pipe at the point of the bend. If there is no internal support, the bending forces exerted on the pipe can cause deformation of the pipe. For example, if unsupported, that part of the inner wall of the pipe which becomes the inside bend may become wrinkled in that area.
Various devices and systems have been developed for use in providing this internal support of the pipe at the point of the bend. One such system is described in U.S. Pat. No. 4,493,203 issued Jan. 15, 1985 in the name of Wheeler et al and entitled: "Resilient Internal Mandrel." In that patent, the internal mandrel includes a urethane plug which is positioned between a piston of a hydraulic cylinder and an end plate. The resilient plug includes a plurality of individual flat discs made of urethane. An hydraulic cylinder is provided. The plurality of resilient flat discs with holes therethrough are supported on tie rods which are supported between the adapter plate cylinder and a first plate spaced therefrom. These flat discs are of uniform size in diameter and uniform thickness. Together with the placement of the tie rods, they become a resilient plug. A circular piston is driven by the hydraulic cylinder. The first circular end plate is used which has an exterior diameter only slightly less than the internal diameter of the pipe to be bent so that the first end plate can move freely through the pipe while maintaining a minimal gap between the outer periphery of the end plate and the interior wall. A second end plate is also provided, and it is rigidly secured to the cylindrical adapter plate. In operation, the resilient plug is inserted into the pipe and is positioned at the point to be bent. Hydraulic power fluid is then provided to the hydraulic cylinder. This pressure causes the piston to move toward the first end plate, thus compressing the resilient flat discs until they contact the internal wall of the pipe being bent. In this system the piston moves away from the cylinder toward the first end plate which is held in a fixed position with respect to the cylinder by the aforementioned tie rods. In this operation the resilient flat discs are compressed which reduces their thickness and at the same time expands them so that the outer edge of the disc contacts the internal wall of the pipe being bent. The pipe is then bent. After bending procedure is complete, the hydraulic piston is then de-pressurized, and the resiliency of the disc causes them to contract and then thus the mandrel can be moved.
The first end plate and the piston are of the maximum diameter which can be easily inserted through the pipe being bent so that extrusion of the resilient material between the edges of the end plate and piston and the wall of the pipe will be limited when the flat disc are compressed.